1. Field of the Invention
The present invention relates to coated pharmaceutical dosage units such as tablets and the like. In particular, the invention relates to an improved method for coating pharmaceutical tablets with an aqueous polymer solution.
2. Brief Description of the Prior Art
Numerous methods for coating pharmaceutical tablets are known. They include sugar coating, solvent film coating, aqueous film coating, delayed release coating and granule coating techniques.
Pharmaceutical tablets have been coated for a variety of reasons, including masking objectionable flavors or odors, protecting unstable tablet compositions, improving the ease with which the tablets are swallowed, providing protection of the tablets through the stomach with enteric coatings and improving the appearance of the tablets. For example, aspirin tablets and other tablets that are powdery and friable have been treated with a variety of coatings to keep them from dissolving too soon.
In the past, sugar coating was the most commonly used coating technique. However, disadvantages of sugar coating such as relatively high cost, long coating time and high bulk have led to the use of other coating materials. Some of the most commonly used coatings today are polymeric film coating agents. Advantages of polymeric coatings include the ability to produce a tablet having a coating that comprises less than 3% of its weight, better resistance to chipping and increased tablet strength. Polymers have been applied to pharmaceutical tablets using both aqueous and non-aqueous solvents.
Various methods for coating tablets with polymeric solutions are known, including rotating pan, fluid bed, spouted bed, coascervation tank and pressing methods. In most coating methods, the coating solutions are sprayed onto the tablets as the tablets are being agitated in a pan, fluid bed, etc. As the solution is being sprayed, a thin film is formed that adheres directly to each tablet. The coating may be formed by a single application or may be built up in layers through the use of multiple spraying cycles.
Rotating coating pans are often used in the pharmaceutical industry. Uncoated tablets are placed in the pan, which is typically tilted at an angle from the horizontal, and the liquid coating solution is introduced into the pan while the tablets are tumbling. The liquid portion of the coating solution is then evaporated by passing air over the surface of the tumbling tablets. In contrast, a fluid bed coater operates by passing air through a bed of tablets at a velocity sufficient to support and separate the tablets as individual units. Once separated, the tablets are sprayed with the coating composition.
Typical spray coating solutions include polymers, plasticizers, dyes and other ingredients dissolved or dispersed in an aqueous or non-aqueous medium. Aqueous systems are preferred due to lower costs and environmental compatability. However, a major disadvantage of conventional aqueous polymer coating methods is that they require relatively long mixing times at high shear rates in order to disperse the polymeric ingredients in water. Such long mixing times are detrimental because they result in significant reductions in processing rates. Furthermore, the high shear rates required for mixing the polymers, and the long times required for such mixing, cause excessive foaming of the solutions, resulting in further time delays while the foam dissipates. Antifoaming agents can be used to reduce foaming problems, but they increase costs.
U.S. Pat. No. 4,302,440 issued Nov. 24, 1981 to John et al. discloses a method for aqueous spray coating hydroxypropyl methylcellulose onto the exterior surface of aspirin tablets. The aqueous solution comprises 2-15 weight % hydroxypropyl methylcellulose and 15-25 weight % plasticizer based on the hydroxypropyl methylcellulose. The solution is sprayed onto uncoated aspirin tablets as they rotate in a baffled pan. This patent and all other patents cited herein are hereby incorporated by reference.
U.S. Pat. No. 4,970,081 issued Nov. 13, 1990 to Frisbee discloses aqueous coating solutions containing an acrylate/methacrylate copolymer, hydroxypropyl methylcellulose, sodium chloride and talc. The solution is coated on aspirin granules to provide controlled release.
U.S. Pat. No. 4,816,264 issued Mar. 28, 1989 to Phillips et al. discloses aqueous coating solutions containing multiple polymers such as hydroxypropyl cellulose and acrylic resin. The solution may also contain other ingredients such as antifoam agents, plasticizers and flavoring agents. The coating solution is used in a rotating pan to coat several different types of drug tablets.
U.S. Pat. No. 5,047,258 issued Sep. 10, 1991 to Belanger et al. discloses a process for spray coating tablets that utilizes an acrylate enteric polymer and plasticizer in water. The spray coating solution requires no anti-adherent such as talc. The spray coating operation is carried out with conventional rotating perforated pans.
U.S. Pat. No. 5,098,715 issued Mar. 24, 1992 to McCabe et al. discloses a method for aqueous spray coating tablets using solutions containing polymer, plasticizer, flavoring and sweetening ingredients. Titanium dioxide or other opacifying agents or colorants may optionally be used in the coating solutions.
U.S. Pat. No. 3,935,326 issued Jan. 27, 1976 to Groppenbacher et al. discloses a process for coating tablets using a synthetic resin dispersed in water.
U.S. Pat. No. 4,572,833 issued Feb. 25, 1986 to Pedersen et al. discloses a method for coating pharmaceutical tablets using organic or aqueous solutions. When an aqueous solution is used, the solution includes a hydrophobic substance such as wax and is applied at a temperature above the melting temperature of the hydrophobic material. A fluidized bed or rotating pan may be used to coat the tablets.
U.S. Pat. No. 4,606,909 issued Aug. 19, 1986 to Bechgaard et al. discloses the use of organic solvents or aqueous solutions for coating pharmaceutical units. The aqueous solutions include acrylic polymers and produce coatings that are insoluble below a pH of 7.
U.S. Pat. No. 4,800,087 issued Jan. 24, 1989 to Mehta discloses a method for microencapsulating pharmaceutical cores using an aqueous polymer coating. In addition to polymers, the coating solution may contain diluents, fillers, bulking agents, plasticizers, pigments and opacifiers.
U.S. Pat. No. 4,556,552 issued Dec. 3, 1985 to Porter et al. discloses a method of spray coating pharmaceutical tablets using a dry powder that is mixed with water to form a coating suspension. The powder comprises polymer, plasticizer, pigment and anticaking ingredients. After the powder is mixed with water, an ammonia solution is added to the suspension, followed by spraying of the suspension onto the pharmaceutical tablets.
U.S. Pat. No. 4,511,553 issued Apr. 16, 1985 to Boesig et al. discloses a coating process using an aqueous solution of saccharose and at least one additional sugar such as lactose. Additional flavors, fragrances, and coloring ingredients may be added to the aqueous solution. The solution may be used to coat pharmaceutical tablets, chocolate centers and hazel nuts.
U.S. Pat. No. 4,704,295 issued Nov. 3, 1987 to Porter et al. discloses a method for coating pharmaceutical tablets utilizing a dry powder that is added to water and then sprayed onto the tablets.
U.S. Pat. Nos. 4,855,326, 4,873,085, 4,997,856, 5,011,532, 5,028,632, 5,034,421 and 5,096,492 issued to Fuisz disclose methods of producing filaments comprising various ingredients combined with a sugar carrier. The filaments are produced by a spinning technique similar to that used for making cotton candy. The ingredients, such as medicaments or cosmetics, are combined with the sugar carrier, and the mixture is then spun to form high aspect ratio fibers.
The present invention has been developed in view of the foregoing and to overcome the deficiencies of the prior art.